I had a finisher try to tell me that the reason why I can see speed bumps on a hallway (almost every joint was humped out bad) Is because the GC asked for a level 4 finish and If he wanted it 100% flat He should have paid for a level 5. I dont know about you guys but a level 4 still needs to be flat it just means you finish the joints, angles, and screws. A level 5 is a tight skim after you achieve a level 4 and sand it. The reason for a level 5 is not to flatten at all just to achieve a consistentcy of all mud so you cant see the difference in texture between the mudded portions of the wall and the paper face of the sheetrock. All in all a level 4 should be flat. Is this just a geographical thing or is it a universal concept?